Although it is well established that a single neural network can generate several related but distinct behaviors, we still do not understand the mechanisms that allow the nervous system to generate multiple behaviors in response to different stimuli. The long range goal of the research presented in this proposal is to understand the neural mechanisms that assure the selection of the appropriate neural output according to the behavioral demands imposed on the organism. We propose to use the well characterized feeding behaviors and its neural substrates in Aplysia in order to extract the principles which relate sensory inputs to the selection and initiation of complex behaviors. We propose to test a hypothesis that this selection can be explained in terms of a combinatorial action of modulatory cotransmitters released from specialized pattern initiating neurons (CBIs) that function as sensory interneurons that funnel sensory information to the pattern generating circuitry. The proposed projects include: 1) identification of specific inputs to the pattern initiating neurons and determination of behaviors in which these cells are active; 2) Characterization of the contribution that these neurons make to specific behaviors; 3) Identification of transmitters and modulators released from these cells; 4) determination of the biophysical and cellular mechanisms of action of the modulators. The research will use an integrative inter- disciplinary approach in which simplified preparations consisting of isolated portions of the nervous system are used in conjunctions with semi-intact preparations that can generate complex behaviors that occur in intact animals. This approach provides assurance of the behavioral relevance of the cellular mechanisms that will be uncovered using a combination of electrophysiological, biophysical, biochemical and molecular techniques. The general importance of this type of research is likely to extend beyond the field of the selection of motor behavior, as combinatorial actions of multiple cotransmitters may be responsible for such phenomena as behavioral arousal and selective attention.